Corrosion resistant chromium alloy manufacture



?atented June 27, 1933 UNITED STATES PATENT OFFICE.

JOHN JOHNSTON, OF SHORT HILLS, jERSEY, ASSIGNOR TO UNITED STATES STEELCORPORATION, OF NEW YORK, N. Y., GORPORATIONOF NEW JERSEY CORROSIONRESISTANT OHROMIUM ALLOY MANUFACTURE No Brewing.

This invention relates to metallurgy and more particularly tochromium-containing corrosion resistant alloys and to methods ofmanufacturing the same.

ltleretofore in the art it has been customary to comprisechromium-containing corrosion resistant alloys of a relatively highproportion of chromium. It is estimated that it requires more than about12 percent of chromium in iron, for example, to impart thereto thecorrosion resisting properties of the chromium. llt is well known thatcarbon is detrimental to the corrosion resisting properties of suchalloys.

This has been attributed to the'fact that chromium forms a relativelystable chromium carbide compound having the empirical formula C146 inwhich approximately one molecular weight of carbon combines withapproximately four molecular weights of chromium or that each unitweight of carbon present in the alloy combines with about sixteen unitweights of chromium. It is apparent therefore that a relatively smallamount of carbon will have a pronounced effect on the chromium contentof the alloy. It is difficult to reduce the carbon content of suchalloys below approximately 0.06%, and it has been found that even suchsmall amounts of carbon may be detrimental to corrosion.

resistant chromium alloys when they are subjected during service toelevated temperatures.

it has been proposed to overcome the detrimental eifect of thisrelatively low and unavoidable carbon content of chromium containingcorrosion resistant alloys by the adnot experienced. Those metals whichhave been proposed comprise titaniumpzirconium, I

tungsten and molybdenum. Of these titanium has been preferred foreconomic and practical reasons and also for the reason that the titaniumcarbide compound formed Application filed June 25, 1931. Serial No.546,921.

does not appear to deleteriously affect the workability of the resultingalloy.

The usual procedure heretofore practiced in the addition of titanium tochromiumcontaining corrosion resistant alloys is toadd the titanium tothe fused corrosion resistant alloy mixture employing an excess oftitanium to ensure the total conversion of the carbon to the titaniumcarbide compound. In some cases it has been suggested to use an excessup to 5 to 10% titanium such an excess of titanium, however, would belargely present as an alloying constituent in the final alloy.

' For some purposes it is desirable to obtain a low-carbonchromium-containing corrosion resistant alloy in which there issubstantially no excess of titanium present as an alloying constituentand in which the carbon content is comprised substantially of titaniumcarbide (or its equivalent). Under prior art methods of forming titaniumcontaining a,l loys, this is not practical.

It is one of the objects of the present in-. vention to obtain such analloy product.

It is another object of this invention to prsovide a method ofmanufacturing such an alio lt is another object of this invention toimprove the method of manufacturing chromium-containing corrosionresistant alloys.

Still another object of this invention is to provide a method ofintroducing relatively small amounts of a highly reactive constituentinto chromium-containing alloys.

Other objects and advantages will become apparent as the invention ismore fully disclosed.

In accordance with the objects of my invention I have found that a largepart of the carbon in chromium-containing corrosion resistant alloys isincorporated therein as a constituent of the ferro chromium alloyutilized in the compounding of the same. It is difficult to obtain asubstantially carbonfree ferro chromium alloy which does not alsocontain deleterious amounts of aluminum, silicon and the likemetalloids.

I have found, however, that if the carbon containing ferro chromium isfirst admixed with titanium (or its equivalent) in such manner as toconvert all or substantially all of the carbon content thereof totitanium carbide, the resultant ferro chromium alloy product may beutilized in the forming of corrosion resisting chromium alloys free fromthe accompanying detrimental carbon effects. I have also found that byproviding an excess of titanium in the term chromium this excess may besubsequently utilized as a carbon fixing agent for the residual carbonin the metal comprising the base for the corrosion resistant alloyproduct without the undue losses heretofore experienced and withoutusinga relatively large excess of the titanium as has heretofore, beennecessary. This is believed due to the fact that the usual residualcarbon oi the alloy base to which the chromium is added is more readilyconverted to titanium carbide than is chromium carbide.

By control analyses and by proper calculation, the total carbon contentof the corrosion resistant alloy may be readily determined and theamount of titanium added thereto as a constituent of the ferro chromiumalloy readily controlled. It is apparent that I may use the titaniumcontaining ferro chromium alone in-the forming of the corrosionresistant alloy. or I may utilize it in part admixed with low carbonferro chromium. if desired. It is preferable, however. to utilize thetitanium containing ferro chromium alone as the chromium carbidecontentthereof has 'been substantially reduced or converted over carbidecompound. Stoichiometrically. the

amoun of the titanium necessary would be approximately four times theamount of the total carbon content of the alloy, but owing to the factthat the carbon content of the alloy base is in a greatly diluted form.it is necessarv to add a somewhat greater amount of titanium. I havefound that in general the amount of titanium added should approximatefrom 6 to 8 times the total carbon present. Amounts in excess of thismaybe construed as being an alloying constituent and for the purposesofthis inventionundesirable. 3

The chromium-containing corrosion resistant alloy products of thepresent invention may be comprised of iron base alloys or of the ironnickel base alloys and may be comprised in part of other alloyingconstituents such as manganese, silicon, aluminum, copper, cobalt andthe like.

As a specific embodiment of the practice of the present invention, Iwill disclose the same as it may be utilized for the preparation of thewell known so-called 18-8 type of chromium-nickel-iron alloy containingapproximately 18% chromium, 8% nickel less than 0.1% carbon and thebalance mainly iron. I prepare the titanium containing low carbon ferrochromium either by melting up low carbon ferro chromium and adding theproper proportion either of titanium or of a mixture of titanium oxideand reducing agent which by reaction yield titanium; or I can mix atitanium ore, such as rutile or ilmenite, or a titaniferous iron ore,each in proper proportion, with the chrome ore from which the ferrochromium is made. The desired chromium nickel iron alloy is then made byadding this modified ferro chromium in the usual way in amountsuificient to yield the desired chromium content, to a melted bath oflow carbon steel to which the proper amount ofnickel has been added. Imay employ the titanium containing ferro chromium in order to reach toproper final content of titanium. This is adjusted on the basis of thetotal carbon present. in the fused alloy so as to be suflicient tocombine with the total carbon to form a titanium carbide compound. Thetitanlum should be preterablyadded in sufficient excess to allow forsuch lossesas may be due to interaction with oxides, nitrides and thelike components of the steel bath but not in sullicient amounts as tobecome thereby an alloying constituent of the steel. An amount in excessofapproximately 68 times-the carbon content of the steel should beavoided. Preferably I adjust the components of the final alloy asclosely as possible to the desired composition with respect to chromiumand nickel, maintaining carbon less than 0.1% but preferablyapproximately 0.06%), and the titanium at least in the proportion ofapproximately four times the weight of the carbon, but preferably from 6to 8times the carbon, and the balance mainly iron.' Residual amounts ofimpurities of manganeseasilicon, aluminum, phosphorus and sulphur areusually present. Manganese or copper may be substituted in part for thenickel, and other alloy constituents such as vanadium and c0- balt, forexample, may be present in various amounts, ifdesired. The siliconcontent may be increased beyond the normal residual ranges but thephosphorus and sulphur impurities should be substantially eliminatecL'Having with particularity broadly and specifically disclosed the presentinvention, it is believed apparent that there may be many modificationsand departures made from the specific embodiment disclosed hereinwithout departing essentially from the naing chromium-nickel steels, themethod ofincorporating titanium therein which comprises addlng the sameas an iron-chromiumtitanium alloy having a low carbon content and atitanium content at least ranging from.

six to eight times the said carbon content. 3. In the manufacture of lowcarbon corrosion resisting chromium-nickel steels, the method ofeffectively eliminating the carbon therefrom which comprisesincorporating therein a proportion of a low \carbonironchromium-titanium alloy, the titanium content thereof being inexcess of that necessary to empirically combine with the said carbon,the proportion of said alloy added being at least sufiicient to bringthe titanium content of the steel to about six to eight times the totalcarbon of said steel.

In Witness whereof, I have hereunto signed my name.

JOHN JOHNSTON.

